The compression ratio depends on the file types. In this case, you should use the zip without compression to speed up the backup.
To do that, please open Backup Properties->Compression
Under "Zip compression" section, delect "Zip without compression" level.

Splitting the backup will speed up the process only if you don't have enough system resources to handle large files.

There isn't a minimum configuration requirement for Backup4all. If your computer supports Windows XP or higher, Backup4all will run fine on it. The backup speed and system usage for large backups depends on your computer performance. The higher computer performance you have, the better results you will get.
You can split the zip file in smaller chunks of 4 GB to get better results.